Quantitative analysis of analytes in fluid samples, particularly bodily fluid samples, often provides critical diagnostic and treatment information for physicians and patients. In solid phase lateral flow and capillary flow assays, certain reagents are attached to a solid surface, facilitating separation of analytes. The solid phase is exposed to a sample containing the analyte; the extent of this binding is quantitated to provide a measure of the analyte concentration in the sample. Transduction of the binding event into a measurable signal, however, is affected by a number of limitations, including constraints of particle movement on the solid phase, which affect the specificity and applicability of quantitative assays. In addition, related analytes may compete with one another in an assay, rendering it difficult to assess correctly the presence of an analyte of interest.